1. Field of the Invention
This invention pertains to drilling of holes through the earth. More particularly, a nozzle is provided for drilling of drainholes from wells and other small-diameter holes.
2. Description of Related Art
There are a variety of reasons to drill small-diameter holes through the earth. For example, fiber optics cable, utility lines, bolt holes in mines and drainholes from wells require such holes.
Drainholes drilled from wells into selected subsurface formations have been widely investigated. U.S. Pat. No. 6,263,984 B1 includes a discussion of jet drill bits and several prior art methods and types of apparatus for drainhole-drilling using fluid jets.
Jet bits for drilling that incorporate a swirling motion to the fluid before or after it is discharged against the rock to be cut are known. For example, U.S. Pat. No. 4,790,394 discloses xe2x80x9ca whirling mass of pressurized cutting fluid .xe2x80x9d The swirling fluid exits a nozzle as a free jet that increases in diameter as it moves away from the nozzle. A variety of mechanical configurations for producing the swirling motion are disclosed. U.S. Pat. No. 6,206,112 B1 discloses vortex generators as part of a drilling apparatus which includes drilling heads at the end of extensible drilling tubes. In one embodiment, the drilling head has a hemispherical nose with a plurality of nozzles that are directed at an angle such as to generate a vortex outside the nozzle as fluid exits.
The use of swirling jets along with mechanical cutters has also been investigated. A spinning jet stream is disclosed in U.S. Pat. No. 5,291,957. The spinning jet stream is developed from a tangentially driven vortex flow system. The stream is used along with an apertured mechanical cutting element that places the exiting spinning jet against a surface to be cut. U.S. Pat. No. 5,862,871 discloses, in one embodiment, a nozzle having a central bore through the housing with discharge of a portion of the fluid passing through the central bore as a swirling stream and part as an axial stream.
Researchers at the University of Petroleum in China have made extensive studies of water jet drilling, including horizontal radial drilling with a swirling water jet (Water Jet Technology in Petroleum Engineering, Shen Zhonghou, Pet. Univ. Press, 1997, Chap. Six, pp. 115-149). Nozzles having vanes to produce a swirling motion of the drilling fluid as it forms a jet were developed. Structural features of the vanes and corresponding axial and tangential velocity distributions in a swirling jet are described in the referenced book. The exit orifices of nozzles investigated were usually 4.0 mm or 6.40 mm in diameter and had a length in the range from 0.5- to 5.0- times the diameter of the orifice. The higher drilling rate observed with a swirling jet compared with a straight jet was explained by the facts that: (1) the cutting action of a swirling jet is influenced more by shear strength of a rock than by its compressive strength, and (2) the shear strength of a rock is lower than its compressive strength. The effect of stand-off distance, i.e., the distance from the jet exit to the rock surface, was investigated and it was found that the advantages of the swirling jet exist in the range of small stand-off distances. Typically, the diameter of the hole cut by the swirling jet was several times the diameter of the jet nozzle. Also, as the rock was cut the depth of the center of the hole was less than the depth around the perimeter of the hole. Drilling rates measured in sandstone at a pump pressure in the range from about 7,000-8,000 psi and at a pumping rate in the range of 100 GPM were in the range of about 14-22 ft/hr, with hole diameters in the range from about 2 to 4 inches (50 to 100 mm). All references cited above are hereby incorporated by reference herein.
What is needed is a jet nozzle that drills a hole through the earth, such as a drainhole, having a diameter large enough for its intended application and large enough to allow cuttings to pass outside the nozzle and the tube to which the nozzle is attached, but that drills the hole rapidly with minimum flow rate and horsepower requirements. The jet nozzle should be attachable to the distal end of a tube that supplies the drilling fluid. Preferably, the nozzle should exert a force in the direction to push the nozzle and tube through rock, but should also drill at a rapid rate without high sensitivity to stand-off distance.
A nozzle is provided for drilling through the earth. The nozzle includes a device for imparting swirling motion to fluid passing through the nozzle before the fluid is discharged through a front orifice. Orifices in the body of the nozzle may be directed toward the inflow end of the nozzle so as to provide a force to drive the nozzle and an attached tube through the hole being drilled. An extension is placed ahead of the front orifice to limit the radius of the swirling fluid discharged from the orifice. Method for drilling through the earth using the nozzle is provided.